There almost has to be a pivot at what would normally be a rigid connection to the seat clamp, which means that the rear of the seat is going to be going up and down with the rear supension swingarm. It also looks like, because of the crank length, the pedals are dangerously close to scraping the ground with each revolution. I'm not even sure I'm seeing a drive chain on this thing.

Methinks this is like so many of the 'lowrider' bikes; made more for show than for go.